1. Field of the Invention
The present invention relates to a control apparatus for a general purpose engine usable in a working machine such as a lawn mower or the like.
2. Description of the Prior Art
First, one example of a prior art automatic choke (auto-choke) device for a small-sized general-purpose internal combustion engine will be described with reference to FIG. 7. The auto-choke device is provided with a carburetor, in which during normal operation, a choke valve 1 is opened as shown by chain lines. In this condition, a negative pressure is generated by descending movement of a piston (not shown) such that air is sucked through an air cleaner (not shown) and a choke bore 2. piston also causes fuel to be sucked and injected through a main nozzle 4. At the same time as the fuel is being injected, the air is being choked by a venturi 3. A fuel-air gas mixture is thus formed and fed into a cylinder (not shown) for combustion therein at a flow rate controlled by a throttle valve 5.
In this carburetor, when the engine is at a low temperature, the fuel fed through the main nozzle 4 often cannot fully vaporize (evaporate), such that the above-mentioned fuel-air gas mixture fed into the cylinder contains surplus air and the gas mixture falls outside of a combustible range. Thus, when the engine is at a low temperature, the choke valve 1 is used to suppress the amount of air so as to avoid the above-mentioned air surplus. It is necessary to change the opening angle of the choke valve 1 depending upon the engine temperature so as to provide the proper gas mixture. For this purpose, a bimetallic element 7 is coupled to the choke valve 1 via a choke rod 6 and the bimetallic element 7 is associated with a heater 8. The bimetallic element 7 serves as a temperature sensor for sensing the temperature of the engine due to the thermal displacement thereof upon change in temperature. The displacement of the bimetallic element 7 is transmitted through the choke rod 6 to the choke valve 1 to change the opening angle thereof. An auto-choke device is thus provided in which a thermal displacement of the bimetallic element 7 is amplified by the heater 8 which is prevented from overheating by means of a current feed control device 9.
Lawn mowers are generally provided with vertical shaft type engines mounted thereon, and are often provided with a single operation lever 21 for control of the engine E. The control provided thereby generally includes the functions of stopping, speed control and choking, as shown in FIGS. 8 and 9.
With reference to FIGS. 8-11, an example of a prior art engine E mounted on a working machine H (e.g. a lawn mower) will now be described. The engine E is mounted on the working machine H as shown in FIGS. 8 and 9, and is provided with a control apparatus for operating a throttle valve and a choke valve (not shown) of a carburetor 23 (FIG. 11) via a Bowden wire 11 by means of an operation lever 21. In FIGS. 8(A) and 8(B) reference numeral 22 designates a spark plug of an engine.
As shown in FIGS. 10 and 11, one example of a prior art control apparatus includes a clamp 12, mounted at one end portion of a control panel 10, for fixedly securing an outer cable 11a of a Bowden wire 11 which is connected to the operation lever 21. The control apparatus further includes a control lever 13 which is rotatably secured to the control panel 10 via a pivot 14 and to which a tip end portion of the Bowden wire 11 is connected, a stop switch terminal 15 disposed on the control panel 10 and adapted to be contacted by the control lever 13, a choke control plate 17 pivotably supported via the pivot 14 and adapted to be moved together with the control lever 13, a rotation adjusting screw 16 mounted on the control lever 13 and adapted to adjustably contact the choke control plate 17, a choke rod 18 connected at one end to a free end portion of the choke control plate 17 and at the other end to a choke lever (not shown in FIGS. 11 and 12) for actuating a choke valve (also not shown), and a governor spring 19 connected between the control lever 13 and a governor lever 24 (FIG. 11). Furthermore, as shown in FIG. 11, the governor lever 24 is fixedly secured to a governor arm 26 mounted in a cylinder block E1 of an engine by means of nuts and the like, and is thereby coupled to a throttle lever via a governor rod 25.
The operation of the above-described control apparatus will now be described. When the Bowden wire 11 is pulled in by the operation lever 21 (FIGS. 8 and 9) so as to rotate the control lever 13 as far as it will rotate in the clockwise direction as viewed in FIG. 10, the control lever 13 comes into contact with the stop switch terminal 15. Such contact with the stop switch terminal 15 results in the engine E being stopped. When the Bowden wire is pushed out so as to rotate the control lever 13 in the counterclockwise direction as viewed in FIG. 10, the governor spring 19 is stretched and the opening angle of the throttle valve in the carburetor 23 is adjusted via the governor lever 24, the governor rod 25 and the throttle lever. During initial and intermediate rotation of the control lever 13 in the counterclockwise direction as viewed in FIG. 10, the control apparatus acts as an engine speed regulating device, but when the control lever 13 is rotated in the counterclockwise direction to an extent where the adjusting screw 16 contacts the choke control plate 17, further rotation causes the choke control plate 17 to also be rotated in the counterclockwise direction as viewed in FIG. 10, such that the choke rod 18 and thus the choke lever in the carburetor 23 are caused to move, thereby causing the choke valve to close and this control apparatus to act as a choke device.
Depending upon various control factors, the clamp 12 may be mounted in alternative locations on the control panel 10 as shown by chain lines at 12'. In this situation, rather than the engine speed being increased by pushing out the Bowden wire 11 with the aid of the operation lever 21 as described above, the engine speed will be decreased by pushing out the Bowden wire.
When choking of the engine E is to be carried out by pushing out the Bowden wire 11 with the aid of the operation lever 21, it is necessary, in order to limit the length of the Bowden wire 11, to limit the mounting orientation of the engine to the two alternatives shown respectively in FIGS. 8(A) and 8(B), due to the fact that the stop switch terminal 15 is mounted in the same direction as the ignition plug 22 of the engine E.
While the above-mentioned prior art control apparatus which employs a bimetallic element (see FIG. 7) forms an automated mechanism which is responsive to engine temperature, displacement of the bimetallic element due to the engine temperature is small. Thus, it is necessary to use a heater to amplify the temperature and an electric current control device to control the heater. This requires the entire apparatus to be relatively large and expensive.
The prior art control apparatus shown in FIGS. 8 to 11 provides choking and speed regulating functions in addition to an engine stopping function. As a result, its structure is extremely complicated, requires considerable time to disassemble, assemble and adjust, and thus, suffers from low operational reliability. Also, since the choking mechanism is actuated via an operation lever, the operator must determine whether the choke should be closed or opened depending on the temperature of the engine based on his experience and a sixth sense. Such reliance on the operator's judgement inevitably results in the inconvenience of having the engine fail to start because the choke is closed when the engine is hot and of needing to repeat the starting operation a large number of times because the choke is open when the engine is cold.
In addition, the necessity of routing the Bowden wire along the shortest route, restricts the orientations in which the engine can be mounted to a working machine. Thus, if a different engine mounting orientation become necessary for maintenance and handling purposes, it has been necessary to prepare a new control apparatus, thereby resulting in low manufacturing economy of an engine.